In the twentieth century, historiographers of socialism have usually paid little attention to the religious ideas of the first socialist schools in France. This stands in stark contrast to contemporary historiographies of socialism and communism, published between the 1830s and 1850s, which had discussed those recently emerged movements against the background of a decidedly religious tradition: socialists and communists were widely regarded as the heirs of a heretical tradition reaching back to the late ancient environment of early Christianity. This tradition was allegedly handed down to medieval and early modern mystical heretics, referred to as illuminés and théosophes, who were thought to be responsible for the French Revolution and, eventually, the emergence of socialism and communism. As strange as this narrative might seem from today's perspective, it was enthusiastically propagated both polemically and self-referentially. While socialists would argue that certain heresies represented a tradition of 'true? Christianity set against a corrupted Church, critics regarded their ideas as sectarian aberrations from the Christian doctrine. Following a genealogical approach, this article discusses the emergence and the meaning of the terms illuminisme and théosophie in the context of the historiography of socialism and communism. It will be shown that central narratives and motifs can be traced back to theological and freemasonic polemics of the eighteenth century, which revolved around disputes about religious legitimacy. Those polemics entered political discourse in the aftermath of the French Revolution in the form of diverse conspiracy theories that sought to explain the social upheavals by the machinations of illuminés and théosophes. Despite the largely fictional character of those theories, they served as important sources for nineteenth-century historiographers. From a historical perspective, this process is not only of interest because it adds a barely noted chapter to the history of socialism and communism by showing its entanglement with the history of religion. It also renders possible new insights into processes of the contingent discursive construction of meaning and identity. (English)